/*
 * #%L
 * The Art of Multiprocessor Programming
 * $Id:$
 * $HeadURL:$
 * %%
 * Copyright (C) 2012 - 2014 Java Creed
 * %%
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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package com.javacreed.examples.concurrent.chapter2;

import com.javacreed.examples.concurrent.appendix.a.ThreadID;
import com.javacreed.examples.concurrent.extra.Figure;

@Figure("2.6")
public class PetersonLock implements Lock {

  // Thread-Local index, 0 or 1
  private volatile boolean[] flag = new boolean[2];
  private volatile int victim;

  @Override
  public void lock() {
    final int i = ThreadID.get();
    final int j = 1 - i;
    flag[i] = true;
    victim = i;
    while (flag[j] && victim == i) {}// wait
  }

  @Override
  public void unlock() {
    final int i = ThreadID.get();
    flag[i] = false;
  }

}
